Graphics that flicker

I am a researcher and use Delphi(5) as a modelling tool. At the moment I try to display a grid of cells that keep changing their status, i.e. change colour. I draw my grid (a group of rectangles) into a TImage. To update the whole grid before displaying the result I have in fact 2 TImage variables one of which is visible while the other one is not. The invisible one is updated to the new status, the visibility properties for the two variable are swapped over and the other one is updated. I hope this make sense.

My Problem is that the image flickers (a lot).

In a a third TImage variable I try to use FillRect() to clear the image before updating it. The result is pretty much the same.

My system is a 2.5GHz PC under Windows 2000 with Delphi 5. Any suggestion of how to get a flicker free image would be very welcome.